This invention relates to the art of automatic adjusters for the hand brake of an automobile disc brake system.
Mechanical adjusters are typically used for eliminating slack in a mechanical actuator used for the hand brake of a disc brake system resulting from wear of the disc pad""s friction material. Known actuators include a spindle fitted to a sleeve nut by a coarse screw thread, whereby one of the spindle or sleeve nut rotates with respect to the other in response to a very low axial force, thereby to adjust the overall length of the actuator.
During assembly, these mechanisms must be assembled into a cavity formed in the brake housing, and the ease of assembly is an important characteristic of any adjuster design.
Further, the adjusting mechanism must be capable of operating with materials of reduced weight, such as a housing made of aluminum. Thus, actuators designed to operate with a housing of materials such as cast iron are not always suitable for use with aluminum housings. One reason is the differences between the casting properties of the different materials, and another is the different wear properties.
For example, the initial shape of a cavity in a housing made of cast iron can be made closer to the desired shape than those formed in an aluminum housing, because a cavity in a cast-iron housing is made by sand casting, whereas a cavity in an aluminum housing is made with a permanent mold, usually made of steel. Sand casing allows more complex shapes than permanent molds and facilitates formation of cavities of greater depth, with the result that the aluminum housing often requires substantially more machining than an iron housing.
Thus, designs for housings made of aluminum have not been able to adopt prior designs outright. One example of a prior adjusting actuator mechanism is that shown in U.S. Pat. No. 5,060,765. This patent shows an actuator of the type having two cam plates that rotate with respect to each other about a longitudinal axis of the actuator. The actuator includes an adjuster that is constructed in two parts for ease of assembly in the housing. The first part of the adjuster is an insert assembly comprising an actuation shaft, which is integral with one of the cam plates, a stationary cam plate, a threaded strut member, a return spring, and a steel insert. The return spring is placed between the front face of the steel insert and the adjustable cam plate, and one end of the insert is attached to the fixed cam plate, thus securing the parts of the insert assembly together.
The threaded strut member is held against rotation by engagement between a radial projection of the strut and a groove in the steel insert. Thus, the housing may be made of a relatively soft material because the steel material of the insert has good wear properties and can withstand the wear caused by the reciprocating motion of the threaded strut. A disadvantage, however, is that reliance on engagement with the insert to prevent rotation of the threaded strut requires assembly as an insert, which complicates manufacture of the part.
In accordance with the invention, a housing made of a light-weight material, such as aluminum, is provided with a cavity that is deep enough to accommodate both of the cam plates and is configured to engage one of the cam plates and a peripheral part of the sleeve to prevent rotation of these elements.
In one arrangement, the housing is configured such that the sleeve nut and the one cam plate are engaged in the same fashion. In one embodiment of this arrangement, the cavity is generally cylindrical but has two or more elongate, axially extending parallel grooves that receive radial, outwardly extending fingers on the sleeve nut and cam plate. The engagement between the groove and the fingers prevents rotation of these elements. In a second embodiment of this arrangement, the cylindrical cavity is provided with at least two, tube-like, radial projections that extend inward to engage grooves in the periphery of the cam plate and sleeve nut.
In another arrangement, the one cam plate engages the housing differently from the engagement between the housing and the sleeve nut. In one such embodiment, the cam plate is provided with an axial projection that engages a hole in the housing while the sleeve nut is provided with radial fingers that engage an axial groove in the housing.
In a further embodiment, the housing is provided with a wear ring made of a material having a hardness greater than that of the housing material to increase wear resistance.